The present invention relates to television broadcasting and reception, and more particularly to a method and apparatus for providing high quality digital sound signals within the audio portion of a standard television signal.
New digital techniques for the reproduction of sound provide performance that is far superior to analog techniques which have been used in the past. An example of high fidelity sound reproduction using digital techniques can be found in the compact disc technology which has recently enjoyed tremendous success as an alternative to photograph records and tapes. Digital recording and playback techniques provide reproduction of music that is extremely realistic and absent from background noise and distortions which have plagued other high fidelity sound reproduction systems currently in wide scale use.
Recent advances in television technology have enabled the transmission of stereophonic sound together with a conventional television picture transmission. Known systems have used analog techniques in connection with the stereophonic sound reproduction. See, for example, commonly assigned and co-pending U.S. patent application Ser. No. 06/816,133 filed Jan. 3, 1986 and entitled "Apparatus and Method for Stereo Television Sound".
A difficulty with providing digital audio in television broadcasting has been the incorporation of the digital signals within the standard television signal without interfering with the video portions of the television signal or appreciably affecting the quality or type of picture reproduced by conventional video circuits. In addition, any television distribution system which transmits digital audio data (such as a cable television system) must be such that the transmitted television signal can be received and reproduced on the millions of television sets already in existence which use conventional analog sound circuits. Thus, such things as the channel width of six megahertz (MHz) for each channel within the television signal spectrum, the aspect ratio of four to three, the video bandwidth of 4.25 MHz, the horizontal and vertical scanning rates of 15.734 kilohertz (KHz) and 60 hertz (Hz), respectively, and the number of scanning lines per frame at 525 cannot be changed, subject to narrow tolerances.
The present invention provides a method and apparatus for incorporating digitized audio data within the second carrier of a standard television signal in a manner such that the signal will be recoverable for reproduction of the transmitted program on black and white and color television sets already in existence.